Remember to get the article right.

das Gefühl, die Empfindung

If you type die Gefühl, that's wrong -- and Duo often tends to keep the article when making a correction, thinking that you got the noun wrong, rather than getting the article wrong. Unfortunately.

I think "Empfindung" (with a "p" after "m") is more frequently used for physical sensations, whereas "Gefühl" tends to be used for the emotional aspects. But the distinction is not very clear-cut; ultimately, it depends on context..